EP0070094B1

EP0070094B1 - Tube mounting for orifice meter

Info

Publication number: EP0070094B1
Application number: EP82302852A
Authority: EP
Inventors: Davis A. Van Scoy
Original assignee: Grove Valve and Regulator Co
Current assignee: Grove Valve and Regulator Co
Priority date: 1981-06-08
Filing date: 1982-06-03
Publication date: 1985-05-08
Also published as: JPS582616A; CA1170858A; DE3263652D1; EP0070094A1; US4380936A

Description

Natural gas is generally sold by volumetric measurement, and one way to measure the flowing gas is by passing it through an orifice of a fixed, predetermined size in order to measure the pressure drop across the orifice. An orifice meter or fitting comprises a housing with flow passages in which a disc with an orifice is supported. The housing, which is installed in a gas pipeline, is provided with pressure taps for measuring pressures immediately upstream and immediately downstream of the orifice. Because the orifice plate is subject to wear by impacting of sand, line scale and other foreign particles in the flowing stream, it must be replaced at frequent intervals to ensure accuracy in measurement.
Existing orifice fittings or meters (US-A-3069129) have housings of the gate valve type comprising a pair of opposed body plates having aligned circular openings and containing a carrier plate in which the orifice plate is secured in alignment with said openings. The valve body hubs have an outer diameter substantially equal to that of the pipeline but, for any given nominal pipeline diameter there may be two or more inner diameters required, depending upon a number of factors which must be considered in gas metering. This generally requires a manufacturer to stock orifice meters without finishing the flow tubes, and then to complete the tubes to prescribed internal diameter and length upon receipt of a customer's order.
It is an object of this invention to provide an orifice fitting which may be manufactured and subsequently fitted with flow tubes of a selected internal diameter. This object is achieved by an orifice meter comprising a housing with a pair of opposed body plates having aligned circular openings therethrough and an orifice plate positioned between said body plates in alignment with said openings, characterised in that it includes upstream and downstream flow tubes of a standard pipeline outer diameter and a selected inner diameter an upstream and a downstream mounting plate secured respectively around said upstream and downstream flow tubes bolt means securing said upstream and downstream mounting plates each to one of said body plates with the inner end of each of said flow tubes extending into the circular opening in the body plate to which it is mounted and means for sealing between the flow tubes and the body plates and further comprising tap ports through said flow tubes at predetermined equal distances from said orifice plate, pressure tap ducts bored laterally through said body plates from the exterior to said circular openings, and recesses in the outer walls of said flow tubes embracing said tap parts to ensure communication with said tap ducts.
Figure 1 is an elevation view of an orifice fitting embodying features of this invention; and
Figure 2 is a vertical section view of the orifice fitting with the orifice in active position.
Referring now to Figures 1 and 2 with greater particularity the orifice meter or fitting 10 of this invention comprises a pair of parallel, steel body plates 12 and 14, which are secured together by a plurality of bolts 16 clamping them against the edges of an oval body band 18 carrying resilient seal rings 20 to form a s,.iled enclosure 21 between the body plates 12 and 14. This is similar to the gate valve structure shown in M.H. Grove, US Patent document US-A-3,069,129.
Slidably carried between the parallel plates 12 and 14 is a gate-like carrier 22, though of annular configuration with an opening 24 therethrough and counterbored at 26 to form an internal shoulder 28. Supported against the internal shoulder 28 is the orifice plate 30 having an orifice 32 therethrough of a predetermined size. An annular axial flange 34 on the orifice plate 30 carries a seal ring 36 to prevent the occurrence of a leak path around the orifice plate 30. As shown, the internal diameter of the axial flange 34, as well as the internal diameter of the carrier opening 24, are substantially equal to the internal diameter of the upstream and downstream flow hubs or tubes 38 and 39.
Carried on each side of the annular carrier 22 is a seat ring 40 carrying a resilient outer seal 42 and a resilient main seal 44. The main seals 44 on opposite sides of the carrier 22 maintain constant sealing engagement with the body plates 12 and 14 so that, in any position thereof, the portion of the orifice carrier 22 radially inside of the main seal rings 44 is in sealed isolation from the remainder of the valve body space 21.
The orifice carrier 22 has a panhandle stem 46 which is pivoted at 48 to a crank arm 50 carried on a sealed, rotatable shaft 52 with a squared end 54 for partial rotation, as by means of a suitable wrench 56 (Figure 1).
Displaced from the flow tube 38 is an orifice plate replacement opening 58, which is of a diameter larger than the outer diameter of the orifice plate 30, but smaller than the diameter of the seat rings 40. This orifice plate replacement opening 58 is normally closed by a closure plate 60 which is bolted at 62 and sealed at 64 to the valve body plate 12. Carried on the closure plate 60 is an inwardly extending annular or circular plug 66, having an inner, orifice plate retaining surface 66a. In the closure plate 60 a vent port 70 which is normally closed by a threaded plug 72.
In operation, with the orifice carrier in the position shown in Figure 2 with the orifice plate 30 disposed coaxially with the flow tubes 38 and 39, the plate 30 is held in position by engagement of the edge of the annular flange with the inner edge of the upstream flow tube 38 and also by the force of the gas flowing in the direction of arrow F pressing it against the internal shoulder 28. Then, as the crank arm 50 is pivoted, to move the carrier 22 upward, the orifice plate 30 is held in place by sliding engagement of its annular flange 34 with the planar inner surface of the body plate 12, and it is held in position as it traverses the replacement opening 58 by reason of engagement with the inner surface 66a of the plug 66.
With the orifice carrier 22 opposing the opening 58, the opening 58 is sealed off from the remainder of the body space 21 by reason of continued sealed engagement of the seal rings 44 with the parallel body plates 12 and 14. Then, the vent plug 72 may be removed to vent just that space within the main seal rings 44 and, thereafter, the cap screws 62 are threaded out for removal of the closure plate 60. In this condition, the orifice plate 30 is fully accessible and the operator may simply reach in, remove it and replace it, with no screws or other attaching means to be unthreaded or threaded. When the plug 60 is replaced, the orifice plate 30 is again held in place without screws or other attaching means.
The flow tubes 38 and 39 generally have an outer diameter D₁, equal to the O.D. of the pipeline (not shown), but the inner diameter D₂ may vary, depending on factors, such as required wall thickness, prescribed ratio of orifice diameter to flow tube diameter, and the like. Then, for each flow tube diameter there is a prescribed flow tube length. Typically, the upstream flow tube 38 must be twenty diameters in length L₁, measured the orifice disc and the downstream flow tube must be 10 diameters in length L₂.
Accordingly, it is an advantage to fabricate the flow tubes separately from the remainder of the orifice 10 and to then install them on customer order. Accordingly, the flow tubes 38 and 39 are welded at 76 to mounting plates 78 which may be bolted and sealed 80, 82 to the body plates 12 and 14.
The flow tubes 38 and 39 are provided with small lateral pressure tap ports 82 and 84, each of which is displaced a precise distance, usually one inch (25.4 mm), from the orifice plate (30). Grooves 86 and 88 around the flow tubes 38 and 39 embracing the pressure tap ports 82 and 84, ensure with pressure ducts 90 and 92 in the body plates 12 and 14. This allows the body tap ducts 90 and 92 to be spaced from the inner wall of the body plates 12 and 14.
Also provided in the upstream body plate 12 are communicating ducts 94, 95 which open into the body space 21 at the bottom thereof, and in the downstream body plate 14 are communicating ducts 96, 97 which open to the outside of the valve body 10, being normally closed by a plug 98. Hence, in the event that there is-any accumulation of sand, lime scale and other foreign particles below the carrier the plug 98 may be removed to blow the area out with upstream pressure to ensure that the foreign particles will not interfere with proper alignment of the orifice plate.
While this invention has been described in conjunction with a preferred embodiment thereof, it is obvious that modifications and changes therein may be made by those skilled in the art without departing from the spirit and scope of this invention, as defined by the claims appended hereto.

Claims

1. An orifice meter comprising a housing with a pair of opposed body plates (12, 14) having aligned circular openings therethrough and an orifice plate (30) positioned between said body plates (12, 14) in alignment with said openings, characterised in that it includes upstream and downstream flow tubes (38, 39) of a standard pipeline outer diameter (D1) and a selected inner diameter (D2), an upstream and a downstream mounting plate (78) secured respectively around said upstream and downstream flow tubes (38, 39), bolt means (80) securing said upstream and downstream mounting plates (78) each to one of said body plates (12, 14) with the inner end of each of said flow tubes (38, 39) extending into the circular opening in the body plate (12, 14) to which it is mounted and means (82) for sealing between the flow tubes (38, 39) and the body plates (12, 14), and further comprising tap ports (82, 84) through said flow tubes (38, 39) at predetermined equal distances from said orifice plate (30), pressure tap ducts (90, 92) bored laterally through said body plates (12,14) from the exterior to said circular openings, and recesses (86, 88) in the outer parts of said flow tubes (38, 39) embracing said tap ports (82, 84) to ensure communication with said tap ducts (90, 92).

2. The orifice meter defined by claim 1 further characterised in that said enlarged recesses (86, 88) are wide grooves around said flow tubes (38, 39).

3. The orifice meter defined by claim 1 or claim 2 further characterised in that it includes a first flush duct (94, 95) in one body plate (12) extending from said recess (86) to the bottom of the body space (21) between said body plates (12,14), a second flush duct (96, 97) in the other body plate (14) extending from said bottom of the body space (21) to the exterior thereof, and a plug (98) normally closing said second flush duct.